Shares in Atlantia, the toll road operator which runs much of the country's motorways, fell 6.3% after news of the collapse.

French President Emmanuel Macron has tweeted a message of sympathy to the people of Italy, writing in both Italian and French. He said France was ready to offer any necessary aid.

How did the structure collapse?

It fell around 11:30 local time (09:30 GMT) during heavy rain. Police reported a violent cloudburst.

"It was just after 11:30 when we saw lightning strike the bridge," eyewitness Pietro M all'Asa was quoted as saying by Italy's Ansa news agency. "And we saw the bridge going down."

Another witness, unnamed, recalled: "We heard an incredible roar and first we thought it was thunder very close by.

"We live about 5km [three miles] from the bridge but we heard a crazy bang... We were very scared... Traffic went completely haywire and the city was paralysed."

One image posted by the regional emergency services shows a truck perched at the end of the surviving bridge section immediately before the drop.

What do we know of the victims?

Giving the death toll of 22, Deputy Transport Minister Edoardo Rixi said the number was likely to rise.

A child was among the dead and at least 13 more people were injured, said the head of the civil defence agency, Angelo Borrelli.

The full horror of the collapse could be seen in aerial video of the scene.

How important is the bridge?

The Morandi Bridge, built in the 1960s, stands on the A10 toll motorway, which serves the Italian Riviera and southern coast of France.

The missing section was dozens of metres in length, and ran across the span of the Polcevera river.

Were there any concerns about the bridge?

Restructuring work on the bridge was carried out in 2016, Reuters news agency reports.

The highway operator said work to shore up its foundation was being carried out at the time of the collapse, and the bridge was constantly monitored.

"It's not acceptable that such an important bridge... was not built to avoid this kind of collapse," Mr Rixi was quoted as saying by Reuters.

Italy's recently installed government has pledged to increase public investment in infrastructure.

The country spent more than €14bn (£12.5bn; $16bn) on its roads in 2006 but that had dropped to less than €4bn by 2010, according to data from the Organisation for Economic Co-operation and Development.

The figures cover spending on new transport construction and the improvement of the existing networks.

Spending started to increase in 2013, when total spend was less than Spain, Germany, France and the UK.